In recent years, cases that multi-functional peripherals are equipped in offices and copy shops are increasing. A multi-functional peripheral (MFP) is an image processing apparatus which has various functions from a scan function (to be referred to as “SCAN” hereinafter) to a print function (to be referred to as “PDL” hereinafter) and a transmission function (to be referred to as “SEND” hereinafter). The MFP normally adopts a unique compression (decompression) method so as to efficiently process image data and to reduce the image memory size.
More specifically, image data in “SCAN”, “PDL”, and “SEND” (scanned image data, PDL image data, and SEND image data) are compressed (decompressed) at their optimal compression parameters. For example, since the scanned image data includes many noise components of a scanner and image deterioration is not conspicuous even when a high compression ratio is selected, it is compressed using compression parameter for the high compression ratio so as to reduce the image memory size. On the other hand, since the PDL image data includes nearly no noise components unlike scanned image data, and image deterioration becomes considerably conspicuous if it is compressed by selecting the same high compression ratio as for scanned image data, it is compressed using compression parameter for a low compression ratio.
Furthermore, the MFP comprises an image composition function, and can generate a composite image when the user superposes a form image (scanned image data or PDL image data) stored in a storage unit in the MFP and newly input scanned image data or PDL image data.
Japanese Patent Laid-Open No. 6-214923 (US Patent Laid-Open No. 2002-0012453-A1) discloses a transmission technique which generates a composite image by compositing PDL image data and scanned image data using the image composition function of the MFP, compressing the composite image, and transmitting the compressed composite image to a host computer connected on the network.
However, the above patent reference 1 describes that the generated composite image is compressed and is then transmitted, but it does not describe about any selection procedure of a compression parameter upon compressing the composite image.
On the other hand, upon compressing composite image obtained by compositing scanned image data and PDL image data, for example, when compression parameter for a high compression ratio is selected in image compression, severe image deterioration occurs in the PDL image data portion of the composite image. Hence, upon compressing the composite image, it is an important issue to select an optimal compression parameter(compression ratio) in correspondence with image data to be composited in terms of image deterioration.